One of the problems commonly encountered in training a baseball player, especially a young, inexperienced player, is that, when fielding line drives and ground balls, he or she has a tendency to watch the batter while tracking the ball in the lower part of the visual field. As the ball approaches the glove, the fielder loses sight of the ball, and will frequently be unable to catch it. On occasion, the ball will strike an unprotected part of the fielder's body, causing injury.
Losing sight of the ball is a major cause of fielding errors by young players, and has been difficult to correct, even with intensive coaching. The problem is experienced not only by infielders and pitchers in fielding ground balls and line drives, but also by outfielders attempting to retrieve ground balls, by first basemen and other infielders attempting to catch low throws, and by catchers when attempting to catch a low pitch or a throw from another player made while a runner is approaching from third base.
For amateur golfers, one of the two most common causes of poor hitting is looking up before the swing is finished. Another cause of poor hitting is moving the head forward of the ball. Golf professionals teach that a player's head must stay “behind the ball”. That is, the player's head must face a location behind the ball at the time of impact. By observing these rules consistently, professional golfers avoid fading and slicing.
Keeping one's eyes on the ball is important, but by itself it does not solve the problem of fading and slicing. Since the eyes are not stationary in the head, it is possible to focus on the ball while rotating the head forward of the ball in the direction of the target during the downswing. The inevitable result is a slice or a fade.
The player will not necessarily be aware of a forward head movement. Often, the only way the player will know that his or her head moved forward is by observing the shot go to the right or left, or by being told of the head movement by a careful observer.